I have my baby clown killifish in with chocolate gouramis, sid loaches, zebra otos, peckoltia plecs,axelrodi rasboras, and a couple dario dario. Nobody bothers the killifish, they take over the whole top of the tank, swimming amongst the floaties. If you want to breed them I could see needing a species only tank. In fact, I am waiting for my males to show their best color, and I am moving one pair off to another tank. Don't believe everything written on the internet about how fish need to be kept. They can coexist with other peaceful species.